Andersson, Jennifer

Abstract [en]

The aim of this master thesis project was to gain knowledge of potential problems in the planned molybdenum separation plant in the concentrator at Boliden Mineral’s mine Aitik. Main focus was on the uncontrollable foaming earlier observed, that caused losses of copper to the molybdenum concentrate and huge problems in the following water treatment process. The project had two major focuses; finding the cause of the uncontrollable foaming and removing it without affecting the molybdenum recovery negatively. The pulp in the planned molybdenum flotation process could be assumed to contain mostly copper concentrate, process water, thio anions and residuals of KAX (collector) and Nasfroth 350 (frother). It was investigated if none, some, or all of above mentioned species contributed to the foaming, possibly together with temperature and time dependencies. To evaluate the problems with foaming, the project was divided into three different parts namely; evaluation of different analytical techniques, designed conditioning experiments and finally flotation experiments. The analytical techniques chosen were UV-spectroscopy, analysis of total organic carbon and quantitative measurement of foaming by a simple gas-sparged column. For the designed conditioning experiments, the software MODDE was used to create an experimental design where the three factors temperature, water quality and amount of depressant (NaSH) was set at low and high levels respectively. During the flotation experiments the influence of activated carbon on foaming and molybdenum recovery was examined. It was concluded that over-dosage of NaSH do not depress foaming, on the contrary, it makes it worse. Also, there was nothing that suggested that KAX caused foaming. It was however difficult to assess the influence of frother on the foaming, with the available analytical techniques, since it was within the same UV-absorbance range as the much larger sulphide ion peak. Activated carbon did decrease foaming significantly, decreased the water content in flotation products and increased selectivity of molybdenum. It was the only parameter tested that gave a significant improvement to the foaming problem. It was also concluded important to maintain a low flow rate of the flotation gas, to avoid excessive foaming.